LECTURE V.

SULPHUR AND PHOSPHORUS.

MATERIALS AND APPARATUS REQUIRED FOR ILLUSTRATING
THE LECTURE.

Specimens of native and artificial sulphur and sulphurets.
Specimens of sulphates.

Burnt bones,-phosphates, native and others.

Phosphorus in cylinders.

Long glass tube for burning phosphorus in a current of air.

Iodide of mercury-precipitated-illustrative of allotropism.

Iodide of mercury on paper heated, and cooled again, illustrative of

allotropism.

Sulphur-ordinary and allotropic.

Schrötter's allotropic or amorphous phosphorus.

Sulphuret of carbon.

Diamond, charcoal, and plumbago.

Sulphuric acid, (A) anhydrous, (B) hydrated.

Sulphurous acid gas.

Sugar and saw-dust,

Cotton-formation of gun-cotton.

Liquid sulphurous acid.

Liquid chlorine.

Sulphur and copper turnings.

Sulphuretted hydrogen.

Phosphoretted hydrogen.

Sulphur in powder burnt over gas flame.

Imperfect combustion of sulphur in limited amount of atmospheric air. Albumen-water and potash.

Solution of oxide of lead in potash.

Silver spoon and boiled egg.

Prove that sulphur exists in bread and in flannel.

PREPARATORY to commencing the subject of his lecture, Professor Faraday directed the attention of his audience to some magnificent specimens of sulphur

yielding materials, belonging to S. Highly, Esq., jun., and placed for examination in the lobby of the Institution.

From an examination of these minerals-remarked Mr. Faraday-you will readily understand how widely diffused is sulphur in the mineral creation. I bring this great manifestation of sulphur before you first, in order that you may observe its most striking, most prominent qualities: however, the chief point of my present lecture, so far as it relates to sulphur, has reference to the hidden, masked, recondite existence of this element in the animal and vegetable kingdom,long overlooked; but which, since it has been pointed out to us by modern chemists, has become so interesting and so important.

Presently I shall have to advert to these minute organic sulphur combinations,-but, as a preliminary, it will be necessary for me to show you a few of the more prominent manifestations of the substance,— to which end I must select my examples from the mineral kingdom. Sulphur exists very largely combined with numerous metals, constituting by direct combinations sulphurets, or sulphides-by indirect combination, sulphates-some beautiful specimens of which you here observe. It also occurs in volcanic countries—native, or pure. Its leading physical characteristics I need scarcely mention, seeing that they are so very familiar; for instance, it would be unnecessary for me to indicate that, under ordinary circumstances, its colour is yellowthat it is brittle when cold-that it is capable of fusion

or volatilisation. There are, however, some highly important and interesting considerations in reference to certain abstruse physical qualities of sulphur, which, not being matters of universal cognisance, require some notice on my part. I must preface my remarks on this subject by stating that sulphur is according to the definition of chemical nomenclature, a simple body; that is to say, it has never yet been resolved into further elements. This distinction between simple and compound bodies is, in all cases, regarded by chemists as most important. Deeply interesting is the train of contemplation suggested by this assumed simple nature of sulphur in connection with the subject of allotropism, -a subject which has frequently, during the past year, been brought under your notice by various lecturers in this theatre, and last of all by Mr. Brodie,—who, in his able discourse, furnished you with numerous examples of its strange manifestations. These previous developments of the subject of allotropism, however, by others, will not absolve me from the duty of bringing it before your notice again,-seeing that it has an intimate relation with the subject of this morning's lecture. The term allotropism is derived from two Greek words, corresponding, as nearly as they bear literal translation into English, with the expression, another state; and is employed for the purpose of expressing the existence of certain bodies in conditions of manifestation different from those which they usually present, although their chemical composition remains the same.

Now, sulphur, I repeat is a simple body; and this circumstance greatly increases our astonishment at its allotropicity or power of existence in two states,for sulphur is in the category of allotropic bodies. So long as we are dealing with compounds, the condition. of allotropism is not so difficult of rational explanation. We can readily assume, in the latter case, that the elements of which it is composed may be grouped together in more than one system; although the number of the elements-no less than their nature— should remain the same. This is not difficult to understand; nor is the assumption of varied grouping irrational; although it may possibly be incorrect, like any other probable hypothesis which admits of no certain line of demonstration; but immediately we come to deal with substances reputed simple, and find them assuming a second condition, our difficulties increase; our grouping hypothesis is no longer applicable; we are left completely in obscurity.

There is more than one indication of the power which sulphur has to present itself under two manifestations. It is susceptible of crystallisation; and crystals of it may be obtained, not merely in two external forms, but these belonging to two different, inconvertible, and incompatible systems. But the most ready and striking means of illustrating the power possessed by sulphur of manifesting itself under two conditions, is furnished by certain phenomena of its melting and subsequent cooling.

Taking a little common yellow sulphur, I melt it in a Florence oil flask, by means of a spirit lamp. Carefully applying the heat it fuses, and the liquid of fusion is then pellucid and transparent. If I pour a portion of this into some cold water, it condenses into the state which it had before melting-that is to say, of common, yellow, brittle sulphur. I now apply a stronger amount of heat, and the transparent, colourless liquid matter suddenly thickens and becomes black; so that the Florence flask may now be inverted without any of the sulphur coming out. If, however, the heat be still increased, the black, tenacious sulphur once more becomes liquid, and gives off a vapour. Now, the vapour of sulphur from this black compound, and its effects, I shall have to bring under your notice by and by. It appears to be endowed with properties different from those possessed by common yellow sulphur-more powerful, more exalted, more energetic; its tendency to react chemically being increased-just as is the chemical tendency of oxygen when it assumes the peculiar state of ozone.

If sulphur in this black liquid state be suddenly poured into cold water, it assumes and retains a very peculiar condition. No longer yellow and brittle, like ordinary sulphur-like the result of pouring into water the first result of fusion-we, however, now produce a substance like strips of india-rubber or gutta percha in its external characteristics, which may be, and is, applied whilst in this condition to take impressions of seals, and